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Decompression Sickness & trapped gas. AHF 2204 Puan Rosdalila Roslan. Decompression Sickness. Henry’s Law. Henry’s Law. The amount of gas in solution is proportional to the partial pressure of that gas over the solution

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decompression sickness trapped gas

Decompression Sickness & trapped gas

AHF 2204


henry s law1
Henry’s Law
  • The amount of gas in solution is proportional to the partial pressure of that gas over the solution
  • As the pressure of the gas above a solution increases, the amount of that gas dissolved in the solution increases
  • Reverse is also true, as the pressure of the gas above a solution decreases, the amount of gas dissolved in the solution decreases and forms a “bubble” of gas within the solution
henry s law illustration
Henry’s Law Illustration

Low pressure equilibrium

Low concentration

Double the pressure equilibrium

Double the concentration

  • Aircraft crew & passengers:

As altitude increases, excess nitrogen will begin to try to escape the body to the lower pressure outside. This results in decompression sickness, which can be very painful and even deadly.

  • Decompression sickness is caused if the persons facing altitude decreases too quickly that makes nitrogen gas bubbles will form in body tissue rather than being exhaled.
  • Rashes, itching, or bubbles under your skin
  • Lymphatic obstruction which can cause localized swelling
  • Musculoskeletal symptoms include joint pain that worsens with movement and commonly involves the elbows and shoulders
  • Nervous system after-effects include paralysis, sensory disturbances, and bladder problems, usually the inability to urinate.
  • Pulmonary symptoms include chest pain, cough, and shortness of breath.

Symptoms usually appear within 1 hour of surfacing but can be delayed up to 6 hours.

Flying in a commercial aircraft after diving may cause "the bends" to develop in the airplane because the cabin pressure is less than sea level pressure

  • Cabin pressurization.
  • Limitation of time at high altitude.
  • As pressure change at altitude its effects certain body areas such the middle ear, parasinuses, gastrointestinal tract, and the teeth. When the gases in these cavities can't equalize with the ambient environment, the gas is considered to be "trapped."
boyle s law1
Boyle’s Law
  • The mechanical responses to changes in pressure are in accordance with Boyle's Law, which states that a volume of gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant.
middle ear overview
Middle Ear: Overview
  • Most often difficulty is experienced on descent in the form of an ear block (barotitis media). An ear block is usually preceded by a fullness in the ear, gradual loss of hearing and eventually pain.
  • Ear block occurs when you cannot equalize the pressure in your middle ear. When there is a problem with the tube, the middle ear volume decreases and pulls the eardrum inward, creating damage and pain.
middle ear causes
Middle Ear: Causes

Middle ear squeezes occur because of obstruction of the eustachian tube.

  • The most common cause is an upper respiratory infection (cold), creating congestion.
  • Other causes of obstruction include congestion caused by allergies or smoking, mucosal polyps, excessively aggressive Valsalva attempts, or previous facial injuries.
middle ear symptoms
Middle Ear: Symptoms
  • Ear fullness,
  • pain,
  • eardrum rupture,
  • disorientation,
  • nausea, and
  • vomiting
middle ear preventions
Middle Ear: Preventions
  • Valsalva maneuver

Valsalva maneuver is performed by closing the mouth, pinching the nostrils closed and blowing air through the nose. This will force air up the eustachian tube and into the middle ear.

  • Make sure you are in good health with no upper respiratory or sinus problems.
  • swallowing,
  • yawning, or
  • tensing the muscles of the throat; this will allow the pressure to equalize
middle ear preventions cont d
Middle Ear: Preventions (cont’d)
  • During sleep, the rate of swallowing slows down. For this reason, it is advisable to awaken sleeping passengers prior to descent for the purpose of permitting them to ventilate their ears.
  • Infants should be given a bottle or pacifier to aid in equalization.
  • Small children can avoid difficulty by chewing gum.
sinus overview
Sinus: Overview
  • The sinuses most often affected by pressure change are the frontal and the maxillary sinuses.
  • These air-filled, rigid, bony cavities lined with mucous membrane are connected with the nasal cavity by means of one or more small openings.
  • When these openings into the sinuses are normal; air passes through these cavities without difficulty. If the openings of the sinuses are obstructed equalization of pressure becomes difficult and the possibility of a sinus block will increase.
sinus maxillary sinuses
Sinus: Maxillary Sinuses
  • When the maxillary sinuses are affected, the pain will probably be felt on either side of the nose, under the cheek bones.
  • Maxillary sinusitis may produce pain referred to the teeth of the upper jaw and may be mistaken for a toothache.
sinus frontal sinuses
Sinus: Frontal Sinuses
  • When the frontal sinuses are affected, the pain will be located above the eyes and usually is quite severe. This type of sinus problem is the most common.
sinus preventions
Sinus: Preventions

Equalization of pressure to relieve pain in the sinuses is best accomplished by use of:

  • the Valsalva procedure, and/or inhalants.
  • Reversing the direction of pressure change as rapidly as possible may be necessary to clear severe sinus blocks.
  • The gastrointestinal tract normally contains variable amounts of gas with pressure approximately equivalent to that of the ambient atmosphere.
  • The chief sources of this gas are swallowed atmospheric air and, to a lesser extent, gas formed as a result of the digestive processes.
  • As gases in the stomach and intestines expand during ascent, extreme discomfort can occur unless there is relief, ordinarily obtained by belching or by passing flatus.
  • The gastrointestinal tract, however, is the area most commonly associated with pain or discomfort upon ascent.
  • This discomfort is caused by the expansion of gas within the digestive tract during ascent.
  • Gas pains of even moderate severity may result in lowered blood pressure.
  • Shock, or syncope, will be the eventual result if relief from distention is not obtained. Immediate descent from altitude should be made to obtain relief.
  • Watch what you eat before you fly.
  • Staying away from foods you know cause you discomfort or pain in the gastrointestinal tract.

Some of the foods that more commonly disagree with individuals are: onions, cabbage, raw apples, radishes, dried beans, cucumbers, melons-or any food that you know causes you problems.

  • Tooth pain (barondontalgia) is the least common.
  • A toothache may occur at altitude during flight.
  • The pain may, or may not, become more severe as altitude is increased, but descent almost invariably brings relief.
  • The toothache often disappears at the same altitude at which it was first observed on ascent.
  • Common sources of this difficulty are abscesses, mechanically imperfect fillings (very rare in occurrence), inadequately filled root canals, and pulpits.
  • Anyone who experiences a toothache at altitude should see a dentist without delay for examination and treatment.